Problem: `_submit_sync` was a deeply nested closure containing
`_solve_turnstile` and the browser-install block as further nesting.
Status events went to stderr, which `run_scraper()` silently discards.
Solution: Extract `_TURNSTILE_JS`, `_solve_turnstile`, `_ensure_browser`,
and `_submit_headless` to module level. Status events (`installing_browser`,
`checking_login`, `logging_in`, `submitting`) now print to stdout as NDJSON.
`submit()` delegates to `asyncio.to_thread(_submit_headless, ...)`.
Problem: lua typecheck flagged missing start_time field on ContestSummary;
ty flagged BeautifulSoup Tag/NavigableString union on csrf_input.get(),
a 3-tuple unpack where _extract_problem_info now returns 4 values in
cses.py, and an untyped list assignment in usaco.py.
Solution: add start_time? to ContestSummary LuaDoc, guard csrf_input
with hasattr check and type: ignore, unpack precision from
_extract_problem_info in cses.py callers, and use cast() in usaco.py.
Problem: problem pages contain floating-point precision requirements and
contest start timestamps that were not being extracted or stored. The
submit workflow also needed a foundation in the scraper layer.
Solution: add extract_precision() to base.py and propagate through all
scrapers into cache. Add start_time to ContestSummary and extract it
from AtCoder and Codeforces. Add SubmitResult model, abstract submit()
method, submit CLI case with get_language_id() resolution, stdin/env_extra
support in run_scraper, and a full AtCoder submit implementation; stub
the remaining platforms.
